Catheter with flat beam deflection in tip

ABSTRACT

A catheter has a deflection beam with rectangular cross-section and a single continuous puller wire for predictable on-plane bi-directional deflection. The puller wire extends through spacers on opposite sides of the beam so the puller wire is maintained a predetermined separation distance from the beam surface. Tubular structures of the catheter body and the deflectable section are fused at a joint by C-shaped brackets mounted opposite surface of the beam to form a hollow body with holes into which thermoplastic materials covering the catheter body and the deflectable section can melt to form interlocking nodes. Elongated beam stiffeners can be mounted on the beam to provide different curve and deflection geometries.

FIELD OF INVENTION

The present invention relates to a medical device for use in the vesselof a patient for the purpose of diagnosing or treating the patient, suchas mapping tissue and/or ablating tissue using radio frequency (RF) orother sources of energy. More particularly, the invention relates to adeflectable catheter having a flat beam for on-plane bi-directionaldeflection.

BACKGROUND

Electrode catheters have been in common use in medical practice for manyyears. They are used to stimulate and map electrical activity in theheart and to ablate sites of aberrant electrical activity. Atrialfibrillation is a common sustained cardiac arrhythmia and a major causeof stroke. This condition is perpetuated by reentrant waveletspropagating in an abnormal atrial-tissue substrate. Various approacheshave been developed to interrupt wavelets, including surgical orcatheter-mediated atriotomy. Prior to treating the condition, one has tofirst determine the location of the wavelets. Various techniques havebeen proposed for making such a determination, including the use ofcatheters with a mapping assembly that is adapted to measure activitywithin a pulmonary vein, coronary sinus or other tubular structure aboutthe inner circumference of the structure. One such mapping assembly hasa tubular structure comprising a generally circular main regiongenerally transverse and distal to the catheter body and having an outercircumference and a generally straight distal region distal to the mainregion. The tubular structure comprises a non-conductive cover over atleast the main region of the mapping assembly. A support member havingshape-memory is disposed within at least the main region of the mappingassembly. A plurality of electrode pairs, each comprising two ringelectrodes, are carried by the generally circular main region of themapping assembly.

In use, the electrode catheter is inserted into a guiding sheath whichhas been positioned a major vein or artery, e.g., femoral artery, andguided into a chamber of the heart. Within the chamber, the catheter isextended past a distal end of the guiding sheath to expose the mappingassembly. The catheter is maneuvered through movements so that themapping assembly is positioned at the tubular region in the heartchamber. The ability to control the exact position and orientation ofthe catheter is critical and largely determines how useful the catheteris.

Steerable catheters are generally well-known. For example, U.S. Pat. ReNo. 34,502 describes a catheter having a control handle comprising ahousing having a piston chamber at its distal end. A piston is mountedin the piston chamber and is afforded lengthwise movement. The proximalend of the elongated catheter body is attached to the piston. A pullerwire is attached to the housing and extends through the piston, throughthe catheter body, and into a tip section at the distal end of thecatheter body. In this arrangement, lengthwise movement of the pistonrelative to the housing results in deflection of the catheter tipsection.

The design described in U.S. Pat. No. RE 34,502 is generally limited toa catheter having a single puller wire. If bi-directional deflection isdesire, more than one puller wire becomes necessary. Catheters adaptedfor on-plane bi-directional deflection are also known. A flat beam isnormally provided to enable deflection on both sides of the beamsweeping a defined plane. However, the puller wire in tension underdeflection often flips over to the other side of the beam, or where thepuller wires are located close to the beam, a large bending moment isrequired to deflect the beam, imposing significant stress on the pullerwires. Moreover, with the puller wires close and tightly constrained tothe beam, adhesion failure or rupture of the puller wire from the beamposes a significant risk of injury to the patient.

The employment of a pair of puller wires to effectuate bi-directionaldeflection also required a number of components that occupy space in aspace-constrained catheter. More components also increased the risk ofcomponent failures. The use of T-bars and/or crimps can unduly fatiguepuller wires and impart shear stresses resulting from skewed or off-axisalignment of puller wires relative to the longitudinal axis of thecatheter, even if by a minor degree.

Moreover, tubular regions of the heart can vary greatly in size. Acatheter of a uniform width along its length may not be well adapted foruse in such tubular regions. For example, a deflectable tip with alarger french size may impede cannulation and tracking in a smallertubular region and a deflectable tip with a smaller French size may notbe stable in a larger tubular region. Moreover, in particular regions ofthe heart, different deflection and stiffness may be required.

Flat beam construction also requires a method to construct a jointbetween the catheter body and the deflectable section in a manner thatprovides support and endurance for torsional and axial loads placed onthe joint in a clinical environment. Abutting ends of tubings coveringthe beam at the joint may separate and detach from each other due toexcessive torsional or axial forces. Any underlying joint supportstructure should facilitate bonding of the tubings.

Thus, there is a desire for a catheter with more deflection variety andoptions, including a deflectable section that employs a puller wireconfiguration that improves durability while facilitating ease indeflection. There is also a desire for a catheter to have a taperedprofile with a wider proximal end and a narrower distal end and a jointbetween the catheter body and deflection section that can providesufficient torsional stiffness and withstand significant torsional andaxial load.

SUMMARY OF THE INVENTION

The present invention is directed to a catheter having a deflection beamand a single continuous puller wire to effectuate predictable on-planebi-directional deflection with less deflection components for reducingcatheter size without compromising functionality, including the abilityto carry, house and support mapping and/or ablation components, such asa multitude of electrodes and lead wires. The catheter includes anelongated catheter body, a deflectable section, a distal assemblycarrying diagnostic and/or therapeutic electrodes, and a control handle.For bi-directional deflection, the deflection beam of the deflectablesection has a rectangular cross section with first and second opposingsurfaces defining corresponding first and second opposing directions ofdeflection. Acting on the deflection beam, the single continuous pullerwire has a U-bend at or near a midpoint of the wire, which is anchoredat a distal end of the deflection beam. Extending proximally therefromare first and second proximal segments of the puller wire which extendin parallel with the deflection beam through the deflectable section onopposite sides of the beam along the first and second surfaces,respectively. The first and second proximal segments further extendproximally through the catheter body and into the control handle whereproximal ends of the puller wire are anchored. To minimize the forcerequired to bend the deflection beam, each proximal segment extendingalong the deflection beam is guided, maintained and/or bounded to thebeam at a predetermined separation distance from the beam surface by aspacer. The spacers also increase durability of the puller wires byproviding a geometry that allows tensile load with minimal shear stress.

Tubular structures of the catheter body and the deflectable section arefused at a joint for exceptional torsional coupling. The joint includesa pair of brackets mounted at or near a proximal end of the deflectionbeam at a transition between the catheter body and the deflectablesection. The pair of brackets, each mounted on an opposite surface ofthe beam, jointly form a hollow body circumferentially surrounding thebeam which supports abutting ends of the tubular structures that areslipped over distal and proximal ends of the hollow body.Advantageously, the hollow body allows lead wires, cables and tubings topass through the joint without interruption, while providing support tothe tubular structures of the catheter body and the deflectable sectionMoreover, each bracket has holes for receiving interlocking fused nodesformed from melted inner layers of each tubular structure during theapplication of heat and pressure, for example, by utilizing a two piecethermal fusing die.

Each bracket may have a curved body in the shape of a half-cylinder witha “C” cross section with two lengthwise edges that are affixed to a sideof the beam. Alternatively, each bracket may have a curved body in theshape of a half-cylinder with an angled rectangular planar portionadjoined thereto, forming a “G” cross-section, with the planar portionbeing affixed to a side of the beam and the lengthwise edge beingunattached and free floating. In the latter embodiment, the partiallyattached half-cylinder body acts as a spring to provide an outwardpressure against the inner layers of the tubular structures duringfusion under heat and pressure to facilitate the formation of theinterlocking nodes.

The beam may have a constant width along its length, or the width maytaper and be narrowed from the proximal end to the distal end so thatthe deflectable section has a tapered profile, enabling the widerproximal end to have better anchoring in larger tubular regions of thepatient's body and the narrower distal end to have bettermaneuverability in smaller tubular regions. The tapering may occurgradually, smoothly and in a linear fashion with no sharp corners, orthe tapering may occur in a nonlinear fashion with steps and corners. Inany event, the brackets mounted on the beam have a corresponding shape,including a corresponding width or diameter that matches the widthdimension of the beam at the locations of the brackets, so as toeffectively support the tubular structures covering the beam.

The beam may also be adapted for different curve and deflectiongeometries by the use of one or more elongated beam stiffeners. Thestiffeners may have different widths and lengths relative to each otherand/or to the beam. They may be affixed to the beam on one or bothsurfaces of the beam. They may be affixed continuously along theirlengths, e.g., by adhesives, or at selected locations, e.g., byresistance spot welding, brazing or laser welding methods. They may alsobe affixed to the beam solely at their or near their proximal ends,depending on the curve and deflection desired.

In one embodiment, a catheter of the present invention includes anelongated catheter body with a first tubular structure having firstcentral lumen, and a deflectable section having a second tubularstructure with a second central lumen and a flat beam extendingtherethrough where the beam divides the second central lumen into afirst sub-lumen and a second sub-lumen. The catheter includes a pullerwire configured with parallel first and second segments connected by aU-bend segment, where the U-bend segment is anchored to the distal endof the flat beam, the first segment extends through the first sub-lumenof the deflectable section and the central lumen of the catheter body,and the second segment extends through the second sub-lumen of thedeflectable section and the central lumen of the catheter body. Thecatheter also includes a compression coil for each of the first andsecond segments extending through the catheter body, where eachcompression coil has a distal end at or near the distal end of thecatheter body so that effectuate deflection initiates distal of thecatheter body. The catheter further includes a pair of first and secondbrackets, each mounted on a respective surface of the beam to jointlyform a hollow body generally surrounding the beam at or near a jointbetween the catheter body and the deflectable section, where a distalend of the catheter body covers a proximal portion of the hollow bodyand a proximal end of the deflectable section covers a distal portion ofthe hollow body.

In a more detailed embodiment, each half-cylindrical bracket has a Ccross section and the pair of first and second brackets form a generallycylindrical hollow body surrounding the beam. Each bracket has aplurality of holes configured to receive interlocking nodes extendingfrom inner surfaces of the tubular structures covering the hollow body.

In another more detailed embodiment, the spacer includes an adhesivelayer applied to each surface of the beam and a tubing affixed to theadhesive layer where the tubing has a lumen through which the pullerwire extends. The layer and a wall of the tubing provide a predeterminedseparation distance between the puller wire and a neutral bending axisof the beam. The layer and the tubing may be bounded to the beam by oneor more heat shrinking tubing.

The present invention includes a method of manufacturing theaforementioned catheter, including wrapping the tubular structure of thedeflectable section in one or more heat shrink tubing to form a tubeassembly, heating the one or more heat shrink tubing to recover aroundthe second tubular structure; and heating the tube assembly to reflow atleast inner layers of the first and second tubular structures to formthe interlocking nodes. The one or more heat shrinking tubings may beremoved after the tubular structures have been sufficiently reflowed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings. It isunderstood that selected structures and features have not been shown incertain drawings so as to provide better viewing of the remainingstructures and features.

FIG. 1 is a top plan view of a catheter in accordance with oneembodiment of the present invention.

FIG. 2 is a side cross-sectional view of a transition section between acatheter body and a deflectable section of the catheter of FIG. 1 inaccordance with one embodiment of the present invention.

FIG. 2A is an end cross-sectional view of the transition section of FIG.2, taken along line A-A.

FIG. 2B is an end cross-sectional view of the transition section of FIG.2, taken along line B-B.

FIG. 2C is an end cross-sectional view of the catheter body of FIG. 2,taken along line C-C.

FIG. 3 is a perspective view of the deflectable section of FIG. 1, shownpartially broken away.

FIG. 3A is a top view of a joint bracket in accordance with oneembodiment.

FIG. 4 is a perspective view of a joint bracket pair in accordance withanother embodiment, as mounted on a deflection beam.

FIG. 4A is a perspective view of one bracket of FIG. 4.

FIG. 4B is a perspective view of another bracket of FIG. 4.

FIG. 4C is an end cross-sectional view of a transition section employingthe joint bracket pair of FIG. 4.

FIG. 5 is a side cross-sectional view of a junction between thedeflectable section and a distal assembly of the catheter of FIG. 1, inaccordance with an embodiment.

FIG. 5A is an end-cross sectional view of the deflectable section ofFIG. 5, taken along line A-A.

FIG. 5B is an end-cross sectional view of the deflectable section ofFIG. 5, taken along line B-B.

FIG. 5C is an end-cross sectional view of the deflectable section ofFIG. 5, taken along line C-C.

FIG. 6A is a top plan view of a distal end of the deflection beamaccording to one embodiment.

FIG. 6B is a top plan view of a distal end of the deflection beam ofFIG. 6A, in an original configuration.

FIG. 6C is a top plan view of a distal end of the deflection beam ofFIG. 6A, as attached to components of the distal assembly, according toone embodiment.

FIG. 7 is a top plan view of a distal end of the deflection beamaccording to another embodiment.

FIG. 8 is a perspective view of a deflection beam with beam stiffenersin accordance with one embodiment.

FIG. 8A is an end cross-sectional view of a deflection beam with beamstiffeners.

FIG. 8B is an end cross-sectional view of a deflection beam with a beamstiffener with a channel.

FIG. 8C is a side elevational view of a deflection beam with beamstiffeners affixed to the beam at their proximal ends.

FIG. 9 is a top plan view of a tapered deflection beam, in accordancewith one embodiment.

FIG. 10 is a perspective view of deflectable section with a tapereddeflection beam with parts broken away, in accordance with oneembodiment.

FIG. 11 is a top plan view of a tapered deflection beam with slopedsections, in accordance with one embodiment.

FIG. 11A is a top plan view of the deflection beam of FIG. 11 withtapered brackets mounted thereon.

FIG. 11B is a side elevational view of the deflection beam and bracketsof FIG. 11A with a reflowed tubular structure shown partially brokenaway, according to one embodiment.

FIG. 11C is a side elevational view of the deflection beam, brackets andtubular structure of FIG. 11B, with heat shrinking tubings prior torecovery and reflowing.

FIG. 12 is a top plan view of a tapered deflection beam without slopedsections, in accordance with one embodiment.

FIG. 12A is a top plan view of the deflection beam of FIG. 12 withbrackets mounted thereon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a catheter having a catheter body(or shaft) and a deflectable distal portion having an elongated flatbeam or “blade” to effectuate precise on-plane bi-directional deflectionwhile maximizing space within the catheter for components including leadwires, puller wires, cables, tubings and any other support members foradvanced distal tip designs. With reference to FIG. 1, a catheter 10 inaccordance with an embodiment of the present invention includes acatheter body 12, a deflectable distal section 14 distal of the catheterbody, and a control handle 16 proximal of the catheter shaft. Thedeflectable section 14 has a tip assembly 15 having, for example, alasso design with a generally circular main portion extending andoriented transversely from a distal end of the deflectable section 14.Bi-directional deflection is effectuated by user manipulation of anactuator 13 provided on the control handle 16 which moves a puller wirethat extends along the catheter from the control handle 16 through thecatheter body 12, and into the deflectable section 14.

With reference to FIGS. 2 and 2A, the catheter body 12 is an elongatedtubular structure 11 comprising a single, central or axial lumen 18. Thecatheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 may be of anysuitable construction and made of any suitable materials. In oneembodiment, the catheter body 12 is multi-layered comprising at least aninner coat or layer 20, and an outer coat or layer 22 with an imbeddedbraided mesh 21 of stainless steel or the like to increase torsionalstiffness of the catheter body 12 so that, when the control handle 16 isrotated, the deflectable section 14 of the catheter 10 rotates in acorresponding manner. The outer diameter of the catheter body 12 is notcritical, but is preferably no more than about 8 French. Likewise thethicknesses of the layers 20 and 22 are not critical.

The deflectable section 14 has a tubular structure 17 with constructionsimilar to the tubular structure 11 of the catheter body 12 except withgreater flexibility. In the embodiment of FIGS. 2 and 2B, thedeflectable section 14 has a central lumen 19 and a multi-layeredconstruction comprising at least an inner coat or layer 24, and an outercoat or layer 26 with an imbedded braided mesh 25 of stainless steel orthe like. The outer diameter of the deflectable section 14 is similar tothe catheter body 12, at preferably no more than about 8 French.

Suitable materials for the layers of the catheter body 12 and thedeflectable section 14 include materials with moderate heat deflectiontemperatures so stiffness of the deflectable section 14 and thus itsdeflection characteristics are not modified by introduction into thepatient's body due to temperature variations. Suitable materials for theinner and outer layers 20 and 22 of the catheter body 12 include Pebaxand Pellethane. Materials particularly suitable for both the inner andouter layers 20 and 24 include lower shore hardness plastics rangingfrom about 25-55D.

Suitable materials for the inner and outer layers 24 and 26 ofdeflectable section 14 include polyurethane or Pebax. In one embodiment,the tubular structure 17 of the deflectable section 14 includes anextruded braided structure, with the inner layer 24 having a thicknessranging between about 0.002 inch to 0.003 inch of natural “sticky”2533-SA-01 PEBAX, then braided with 0.0016 inch diameter, PEN braid(50-80 pies per inch), and the outer layer 26 including extruded PEBAX5533-SA-01 or 4033-SA-01 PEBAX with about 25% barium sulfate added forradiopacity.

Extending through the length of the deflectable section 14 is anelongated support structure configured as a flat beam or “blade” 30 witha rectangular cross-section R having a greater width W and a lesserthickness T, as shown in FIG. 2B, defining two opposing rectangular facesurfaces FA and FB (or sides, used interchangeably herein) that are flatand smooth, and two outer longitudinal side edge surfaces E1 and E2 thatare friction-inducing, e.g., uneven, rough, textured and/or serrated.The beam 30 may be constructed of any suitable high yield strengthmaterial that can be straightened or bent out of its original shape uponexertion of a force and is capable of substantially returning to itsoriginal shape upon removal of the force. Suitable materials for thebeam include full hard, cold worked stainless steel alloys (304 or 316full hard condition), nickel/titanium alloys (nitinol) or phosphorbronze alloys. Nitinol alloys typically comprise about 55% nickel and45% titanium, but may comprise from about 54% to about 57% nickel withthe balance being titanium. A suitable nickel/titanium alloy is nitinol,which has excellent shape memory, together with ductility, strength,corrosion resistance, electrical resistivity and temperature stability.The width W of the beam generally equals the inner diameter of thedeflectable section 14. Accordingly, the beam 30 is situated inside thedeflectable section 14 to effectively divide or bisect the central lumen19 into two sub-lumens, e.g., equal half cylindrical spaces 19A and 19B,with components such as lead wires, cables, and tubings passing througheither space.

The catheter 10 has exceptional torque transmission capability providedby a joint or transition section 65 between the catheter shaft 12 andthe deflectable section 14, as shown in FIGS. 2, 2A and 2B. Thetransition section 65 transfers torsional forces from the control handle16 to the distal assembly 15 with high fidelity and low hysteresis, toprovide a user with a means to accurately place and control the distalassembly 15 within the patient. The transition section 65 includes apair of opposing, elongated half-cylindrical members or brackets 66A,66B, e.g., formed by die cutting or acid etching, with circularperforations or punched through-holes 68 arranged in a predeterminedpattern. In one embodiment, there are 11 through-holes and the patternincludes a plurality of transverse rows, with adjacent rows offset by apredetermined distance, although it is understood that other alternatingor offset patterns would be suitable, as well. In the illustratedembodiment of FIG. 3A, the pattern has rows R1, R3, R5 and R7 with twothrough-holes each, and rows R2, R4 and R6 with one through-hole each,where rows R2, R4 and R6 are offset from rows 1, 3, 5 and 7 by about thediameter of a perforation. The brackets 66A, 66B can be constructed ofthe same material as the beam 30 and may be pre-coated with an adhesivefor higher bond strength during heat fusion.

In the illustrated embodiment, each bracket has a uniform semi-circularor “C” shape cross section along its length and is affixed at its outerside edges 69, e.g., by laser welding 73, to a respective side of thebeam 30. Having a curved or semi-circular cross-section, the C brackets66A, 66B provide structural support to abutting ends of the tubularstructures 11 and 17 at the transition section 65. In the illustratedembodiment, the brackets 66A and 66B are affixed to the beam 30 near theproximal end 30P (which extends a short distance proximally past thejoint 65 between the catheter body 12 and the deflectable section 14).So affixed, the members 66A and 66B along with the side edges E1 and E2form a full cylindrical hollow body 66 (FIG. 3) with a circumferentialcontour substantially encircling the beam 30 at the transition section65. As best shown in FIG. 2B, the full cylindrical body 66 (usedinterchangeably with the brackets 66A, 66B) defines a central lumen 67that is bisected by the beam 30 into two semi-circular cavities 67A and67B through which components, such as lead wires, cables, etc., canpass.

With reference to FIGS. 2 and 3, in assembling the catheter and thetransition section 65, a distal end 11D of the tubular structure 11 ofthe catheter shaft 12 is slid onto proximal end 66P of the cylindricalbody 66. A proximal end 17P of the tubular structure 17 deflectablesection 14 is slid onto distal end 66D of the cylindrical body 66, withthe beam 30 extending through the lumen 19 of the deflectable section14. Accordingly, distal end of the tubular structure 17 and proximal endof the tubular structure 11 cover the body 66 from opposite directionssuch that they abut each other at or near a mid-location along thelength of the body 66, which can range between about 5 mm and 12 mm,preferably about 6.5 mm and 10 mm.

The inner coatings 20 and 24 of the tubular structures 11 and 17,respectively, are then fused to the body 66, with application ofsufficient heat and pressure so as to melt and flow into theperforations 68 forming nodes 20N and 24N. The fusion creates a verystrong interlocking bond between the tubular structures of the cathetershaft 12 and the deflectable section 14. The nodes 20N and 24N increasethe axial load capacity to the joint 65. In fact, the resulting torquetransmission bond joint can be stronger in torsion and tensile forceloading than the braided catheter body 12 and deflection section 14 thatare bonded to it. The friction-inducing edges E1 and E2 of the beam 30within and in contact with the body 66 also help grab the inner layers20 and 24 and prevent slippage between the beam 30 and the tubularstructures 11 and 17.

To facilitate the application of heat and pressure to the transitionsection 65, one or more protective heat-shrink tubing 70 (FIG. 2), e.g.,fluorinated ethylene propylene (FEP) or polyethylene terephthalate(PET), is placed and shrunken (or “recovered”) over the transitionsection (e.g., by a heat gun or oven). The transition section 65 coveredby the heat-shrink tubing(s) 70 is then placed in a two-piece heatfusing die head (not shown) for heating to melt (or “reflow”) the innerlayers 20 and 24 into the perforations 68, followed by cooling. Theshrink tubing 70 can be used as a process aid to prevent the meltedlayers from contacting the heated die and create a uniform transitionbetween mating ends of the deflectable section 14 and the catheter body12. Thus, the shrink tubing 70 is removed from the transition section 65after the fusing process.

The heat fusing die head utilizes a highly accurate fusing die heightmeasurement indicator (LVDT) to sense fusing die head movement duringthe heating/fusing process. Since the construction materials of thelayers of the shaft 12 and the deflection section 14 may includeextruded raw thermoplastic polymers with a wide range of heat histories(±25° F.) between material lots, monitoring the softening of thepolymers and the resultant die head movement is another means besidestemperature measurement to achieve process control while reducing theinfluence of polymer heat history during the heating/fusing process.Moreover, the transition section can be created in minimal duration(e.g., less than about 60 seconds) using a thermal fusing machine thatis water-cooled to provide fast cycle times. The resulting transitionsection is advantageously homogenous and seamless. The structure isnondiversified once heat-pressure fuse operation is completed.

In an alternate embodiment as shown in FIGS. 4-4C, each elongatedhalf-cylindrical bracket 66′A, 66′B includes a planar portion 63A, 63Bthat is flat and rectangular. The planar portion is adjoined to therespective half-cylindrical bracket along a longitudinal side edge 69 ata nontangential angle θ (FIG. 4A) of about 90 degrees measured betweenthe planar portion and a tangent T off side edge 69. Accordingly, eachmember 66′A, 66′B has a uniform cross-section along its lengthresembling a horizontal letter “G”. The G brackets 66′A and 66′B withtheir respective planar portions 63A and 63B can be formed from a singlerectangular piece of die cut sheet that is bent along the longitudinalside edge 69A or 69B. In the illustrated embodiment, the G brackets 66′Aand 66′B are affixed to the beam 30 near its proximal end 30P (FIG. 4)with each member opposing each other from opposite sides FA and FB ofthe beam 30. Each portion 63A, 63B is affixed to a respective surfaceFA, FB, e.g., by weld 73, leaving free edge 61A and 61B unattached andfree floating. In the illustrated embodiment, the width of each planarportion 63A, 63B is about half the diameter of a half-cylindricalbracket 66′A, 66′B.

Opposing and upside down from each other, the G brackets 66′A and 66′Bjointly form nearly a full cylindrical body 66′ (with the exception ofthe unattached edge 61A and 61B) substantially encircling the beam 30 atthe transition section 65, with the planar portions 63A, 63B extendingdiametrically toward each other sandwiching the beam 30 therebetween.The portions 63A, 63B are thus parallel to each other, and parallel andcoplanar with the beam. The body 66′ (used interchangeably with thehalf-cylindrical brackets 66′A, 66′B) defines a central lumen that isbisected by the beam 30 (and the portions 63A, 63B) into twosemi-circular cavities 67′A and 67′B through which components, such aslead wires, cables, etc., can pass. So joined, the members 66A′, 66′Band the beam 30 have a cross-section resembling the letter “S”. Becauseonly the planar portions 63A, 63B are affixed to the beam leaving edges61A, 61B free floating, each half-cylindrical bracket 66′A, 66′B acts asa “spring” to provide an outward force when pressed on by the innerlayers 20 and 24 during heat recovery of the heat shrinking tubing 70and the reflowing of the inner layers 20 and 24. The outward forceensures larger and deeper nodes 20N and 24N and therefore a better bondbetween the G brackets 66′A and 66′B and the tubular structures 11 and17 of the catheter body 12 and deflectable section 14. The planarportions 63A and 63B provide large flat surface areas for clamping the Gbrackets 66′A and 66′B and the beam 30 together to provide a bettersetup in preparation for resistance or laser welding these componentstogether in terms of minimizing the gap between the welded surfaces andenabling axial alignment between the beam and the brackets. The largeflat surfaces also ensure better contact between contact surfaces of theplanar portions 63A and 63B and the beam 30 for a better and strongerweld.

An accordance with a feature of the present invention, the catheter 10provides bi-directional deflection with a single continuous puller wire28 that advantageously requires less actuation force by a user andimposes less shear stress on the puller wire. The puller wire 28 has aU-bend mid-portion 28M being a distal-most portion of the puller wire inthe catheter. As shown in FIG. 5, the U-bend mid-portion 28M divides thepuller wire into two longitudinal portions 28A and 28B of generallyequal length, each with a proximal end that is anchored in the controlhandle 16. With reference to FIGS. 6A, 6B and 6C, to anchor the U-bendportion 28M at a distal location on the catheter, a distal end of thebeam 30 has a receiving formation 32 e.g., either an on-axis slit 32S oran on-axis through-hole 32H, which securely receives the mid-portion 28Mso that each long portion 28A and 28B extends longitudinally centered onthe beam along a respective face surface FA, FB of the beam 30. Thisarrangement advantageously avoids the use of conventional T-bars, crimptype connections, soldering or welding as a means to anchor a distal endof the puller wire to the beam 30. And, because the puller wire is notrigidly attached to the beam 30, this arrangement provides smoothbi-directional steering.

As illustrated in FIGS. 6A and 6B, the distal end 30D of the beam 30 hasan original configuration prior to assembly of the catheter andattachment of the puller wire 28, which includes an elongatedlongitudinal closed slit 32S with a distal end 31 and a proximal end 33.The slit 32S is disposed immediately proximal of a distal end portion30D of the beam 30. The through-hole 32H is disposed in the distal endportion 30D. The U-bend mid portion 28M of the puller wire may beinserted and hooked through the hole 32H, or alternatively in the slit32S at its proximal end 33. In the latter regard, the slit 32S isadapted into an open configuration (FIG. 6C) from a closed configuration(FIG. 6A) for receiving the U-bend mid-portion 28M when the distal endportion 30D of the beam is detached by a user bending or cutting along atransverse “pre-cut” groove 52 (FIG. 6A) provided on the face FA of thebeam 30 proximal of the hole 32H. In the illustrated embodiment, a firsttransverse groove 52 a is aligned with the distal end 31 of the slot 32and a second (half width) transverse groove 52 b is aligned at or near amidpoint along the length of the slot 32S. Thus, the distal end portion30D can be readily broken off or otherwise detached from the beam alongthe groove 52 a. For easier access to the open slit 32S, portion 30 acan be detached from the beam 30 along the groove 52 b, as shown in FIG.6C. The puller wire portions 28A and 28B extend proximally alongopposites sides FA and FB of the beam 30 through the deflectable section14, the central lumen 18 of the catheter body, and into the controlhandle 16.

As shown in FIG. 6C, the slit 32S is generally longitudinally centeredand on-axis with the longitudinal axis of the beam 30 such that the slitdivides the beam into two generally equal elongated sections or prongs54 a, 54 b. In the illustrated embodiment, a hollow tube or ferrule 60(e.g., of stainless steel) is affixed e.g., by laser welding, to face FAof the prong 54 b (although it is understood that the tube 60 may bealternatively affixed to prong 54 a, with the portion 30 b detached fromthe beam). A proximal end of a support member 72 supporting the distalassembly 15 is inserted and anchored in the tube 60, e.g., by crimping,to create an interference fit between the tube 60 and the support member72 to transmit torque and tension/compression forces from the beam 30 tothe distal assembly 15. A mechanical crimp process eliminatesproblematic adhesive bonding that can loosen or fail causing the distalassembly 15 to spin. A servo process with precision force control isused to detect a defined force slope so that acceptable interferencebetween the support member 72 and the tube 60 is created withoutdamaging the puller wire 28.

Proximal ends of the portions 28A and 28B are anchored in the controlhandle 16 and deflection mechanism in the control handle 16 responsiveto the actuator 13 manipulated by a user is configured to draw orotherwise act on a proximal end of puller wire portion 28A or 28 todeflect the distal section 14 with a distinct curvature on side FA or FBof the beam 30. Throughout the catheter body 12, each puller wireportion extends through a respective compression coil 62A and 65B (FIGS.2, 2C and 8) which is flexible but resists compression so thatdeflection of the catheter initiates at or near distal ends of thecompression coils. Along the beam 30 in the deflectable section 14, eachpuller wire portion may be coated with PTFE or Teflon so the pullerwires can slide smoothly inside a respective protective spacer tube 36provided on a respective side of the beam 30 as discussed in furtherdetail below.

As understood by one of ordinary skill in the art, the puller wire 28 isin tension to create a bending moment to deflect the beam 30 in thedesired direction. Conventional catheter with a flat beam may use apuller wire with a rectangular cross-section that is welded and tightlyconstrained to the beam to prevent adhesion failure. While this designmay be simple and compact in certain respects, the puller wire is undersignificant force due because of its close proximity to the beam, whichin pure bending requires a substantial bending moment stress duringdeflection. In contrast, as illustrated in the drawings, including FIG.2B, the catheter of the present invention is configured to provide aspacer of a predetermined thickness to separate the puller wire 28 and aneutral bending axis NA of the beam 30 by a predetermined distance so asto lower the force on the puller wire, including the bending moment.Moreover, the catheter 10 includes a puller wire 28 with a circular (orat least round) cross section to reduce the area moment of inertia, asan otherwise rectangular puller wire with the same cross-sectional areaseparated from the neutral axis by a comparable spacer would undulyincrease the size/diameter of the catheter and the area moment ofinertia to result in an unacceptably stiff catheter.

As shown in FIG. 2B, the spacer on each side of the beam 30 may includea spacer adhesive layer 34 and a wall of a lumened elastomeric pullerwire spacer tube 36. The adhesive layer 34 may be provided by an ultrahigh temperature adhesive transfer tape sold by 3M under the model100HT. The adhesive layer may have a thickness of about 0.001 inch andrequire about 72 hours to achieve full adhesive bond strength. Thespacer tube 36, which may be constructed of polyimide, thin wallpolyetheretherketone (PEEK), nylon or other thin wall thermoplastictubing, is affixed to the adhesive layer 34, and a respective pullerwire proximal portion 28A or 28B extends through lumen 37. An interiorsurface of the lumen 37 surrounding the puller wire may be coated withpolytetrafluoroethylene (PTFE), e.g. TEFLON or TEFLON composite, toreduce static and dynamic friction with the puller wire. On each side FAand FB of the beam 30, the spacer runs longitudinally generally betweenthe receiving formation 32S or 32H (FIG. 6A) and a proximal end 30P ofthe beam 30 (FIG. 2). Alternatively, the spacer may include an extrusionsurrounding each puller wire portion. The extrusion may be made of PEEK.

The round puller wire 28 has a diameter D ranging between about 0.007inch and 0.009 inch, and preferably about 0.008 inch. The beam 30 has athickness T of about 0.004 inch and 0.007 inch, and preferably betweenabout 0.005 inch and 0.006 inch. The puller wire and the neutral axisare separated by a distance d, ranging between about 0.008 inch and0.025 inch, and preferably between about 0.010 inch and 0.015 inch. Inone embodiment, the puller wire diameter D is 0.008 inch and a Nitinol304V wire, and the beam thickness is 0.005 inch.

To constrain and secure the puller wire 28 on the beam 30 and as anadditional means to prevent adhesive failure and detachment, at least afirst inner heat shrink tubing 38 is placed on the beam 30, covering andsurrounding the spacers on both sides FA and FB of the beam 30,inclusive of the puller wire portions 28A, 28B trained through thespacers (hereinafter referred to as “the beam assembly”). In theillustrated embodiments, including FIGS. 2B and 6A, the first inner heatshrink tubing 38 is followed by a second outer heat shrink tubing 39that is placed over the beam assembly to surround and seal thecomponents and the first heat shrink tubing 38. The first heat shrinktubing 38 may constructed of high temperature resistant polyester (PET)or fluorinated ethylene propylene (FEP) and have a wall thicknessranging between about 0.0005 inch and 0.004 inch, and preferably betweenabout 0.00015 inch and 0.001 inch, in an expanded state. Anothersuitable material is polyester in terms of thin wall and high strength.The first heat shrink tubing 38 is recovered by heating with a hotair-based heating system thus providing a second bonding structure forthe spacer tubes 36, as well as a first sealing structure for theadhesive layers 34 and spacer tubes 36. The uneven longitudinal edges E1and E2 of the beam 30 help grab and secure the first heat shrink tubing38 so it do not migrate or slip during deflection.

The second heat shrink tubing 39 may be constructed of extruded naturalPEBAX, e.g., 2533-SA-01 (22D shore hardness), thin wall with a thicknessranging between about 0.002 inch and 0.003 inch, or natural PELLETHANE(e.g., 80A shore hardness). The second heat shrink tubing 39 may be alayer of “sticky” low shore hardness thermoplastic elastomer which isheated and recovered over the first heat shrink tubing 38, thus creatinga second layer sealing structure and a “sticky” heat bondable outerlayer surrounding the beam assembly. The sticky outer layer provided bythe second heat shrink tubing 39 is well suited to bond with the tubularstructure 17 of the deflectable section 14 through a resistive heatingprocess with clamp members to heat the beam 30.

The heat shrink tubings 38 and 39 extend from the distal end 30D of thebeam to near the distal end of the brackets 66A, 66B, so as not tointerfere with the weld 73 between the 66A and 66B and the beam 30.Depending on the length of the beam proximal of the brackets 66A, 66B,heat shrink tubings may be provided there as well.

In another embodiment as illustrated in FIG. 7, a pair of tensile fibers29, e.g., VECTRAN cords are utilized instead of puller wires. A crimpedmetal tube 31, e.g., of stainless steel or other alloys) is attached tothe distal end of each fiber 29. Each tube 31 is affixed, e.g., byresistance- or laser-welded, to the longitudinal center of a respectiveside of the distal portion 30D of the beam. A respective spacer tube 36surrounds each fiber and is bonded to a respective surface FA or FB ofthe beam by a spacer adhesive layer 34. The fibers 29 may be coated withlow density polyethylene or TEFLON, e.g., DUPONT TRASYS 9825 or TRASYS426 and MCLUBE 1829 TEFLON based coatings, to damp out noise and preventstick-slip type non-uniform motion created by variations in dynamic andstatic friction coefficients during deflection. Food grade damping gel(e.g., Nye Lubricants fluorocarbon Gel 835C-FG//874//880FG) havingsynthetic hydrocarbon and PTFE or silicone and PTFE to coat the fibers29 and interior of the spacer tubes 36.

Where the deflectable section 14 has a length greater than about 90 mm,one or more elongated flat beam stiffeners 80 may be mounted to eitheror both sides FA and FB of the beam 30 to modify and obtain desiredcurve geometry when the puller wire or tensile fibers (collectivelyreferred to as “puller members”) are activated via the control handle16. As shown in FIGS. 8, 8A, 8B, 8C, one or more stiffeners 80 may beadhesively bonded to the beam 30. The stiffeners 80 are generallyparallel with the beam 30 and can have similar or different lengthsrelative to each other and the beam. The stiffeners may be bonded by alayer of adhesive 81 (FIGS. 8A and 8B), e.g., applied via ultra hightemperature adhesive transfer tape sold by 3M under the name 110HT. Theadhesive may have a layer thickness of about 1.0 mm. The adhesiveprovides a viscoelastic bond between the stiffeners and the beam.Alternatively, the stiffeners 80 may be spot welded by laser to the beamat selected locations 82 as shown in FIG. 8. It is understood that thesetwo different bonding methods provide different degrees of stiffnessdespite employing beams and stiffeners of the same thicknesses due tothe viscoelastic behavior of the adhesive bond compared to themetal-to-metal fusing of the spot welding bonds.

In yet another alternate embodiment of FIG. 8C, proximal ends 80P of thestiffener beams 80 may be bonded to and rigidly supported by the beam 30at or near the brackets 66 of the transition section 65, leaving distalends 80D of the stiffener beams free floating and unattached, to createanother type of curve. Moreover, depending on the shape and size of thestiffeners 80, a longitudinal channel 84 (FIG. 8B) to accommodate thepuller wire and the spacer.

The cross section of the beam itself may change along its length. Asillustrated in FIGS. 9, 11 and 12, each of beams 130, 230, 330 have atapered configuration with the width W decreasing (continuously ordiscontinuously) from their proximal ends 130P, 230P, 330P to theirdistal ends 130D, 230D, 330D. The narrower distal end facilitatescannulation and tracking through smaller tubular regions, such as thegreat cardiac vein, and the larger proximal end provides more stabilitynear larger tubular regions, such as the coronary sinus ostium whentracked inside the coronary sinus. The width of the beam may begradually tapered, for example, in a linear manner, for a generallysmooth profile along its side edges E1 and E2 (FIG. 9), or it maystep-tapered in a manner along its length, with linearly sloped portions(FIG. 11) or without sloped portions (FIG. 12). It is understood thatthe beam may be constructed from multiple beam segments fused togetherend to end or as a single continuous elongated body. In one embodiment,the distal section 14 supported by the beam may have a proximal sectionwith a 7 french diameter, a mid-section with a 6 french diameter and adistal section with a 5 french diameter.

In the embodiment of FIG. 9, where the beam 130 has the graduallytapered width, one or more pairs of brackets 166A and 166B are affixedto the beam 130 at selected locations forming generally a generally fullcylindrical body encircling the selected locations. The selectedlocations for affixation of brackets (C or G brackets) may be a jointbetween beam segments and/or a joint where the width of the beamchanges. The diameters of the brackets along their lengths varycorrespondingly with the changing widths of the beam at those selectedlocations.

In the embodiment of FIGS. 10 and 11, the beam 230 has a step-taperedconfiguration with rectangular sections 230D, 230M, 230P adjoined bysloped sections 231 therebetween. Each rectangular section has arespective width which is uniform throughout that section. However, themore distal rectangular sections have smaller widths than the moreproximal rectangular sections such that WD<WM<WP where WD is the widthof the most distal section 230D, WM is the width of the mid section 230Mand WP is the width of the most proximal section 230P. Between eachrectangular section is a sloped section 231 whose width changes linearly(by decreasing in the distal direction or increasing in the proximaldirection) along its length so that the sloped section 231 bridges theadjacent rectangular sections 230 without sharp bends or corners on sideedges E1 and E2 of the beam. The slope of each section as measuredrelative to the longitudinal axis of the beam ranges between 0 and lessthan 90 degrees, preferably between about 15 and 30 degrees. In theillustrated embodiment, the beam 230 includes three rectangular sections230 and two sloped sections 231 in between and alternating with therectangular sections 230. As shown in FIGS. 11A and 11B, a pair ofbrackets 266A and 266B (266B not shown) are mounted on each taperedsection 231 forming generally a full cylindrical body encircling eachtapered section. Each pair of bracket conform with their respectivetapered section 231 with a diameter that also changes along its lengthso as to be similarly tapered as the respective section 231.

Alternatively, in the embodiment of FIGS. 12 and 12A, the beam 330 has anonlinear or step-tapered configuration having rectangular sections 330directly adjoined to each other without sloped sections. Thus, the sideedges E1 and E2 have a “step” profile with corners 331. Rectangularsections 330D, 330M and 330P have uniform widths WD, WM or WP,respectively, wherein WD<WM<WP. A pair of brackets 366A and 366B (366Bnot shown) are mounted at or near each corner 331 forming a generallyfull cylindrical body overlapping the distal end and proximal end ofadjacent pairs of rectangular sections 230. The diameter of each bracketmay be uniform along its length and conform with the narrower width ofthe adjacent pairs of rectangular sections 231.

A method of assembling a tapered beam, for example, the beam 230 isdescribed below in reference to FIG. 10, although it is understood thatthe method may be used for any beam, including the beam 130 or the beam330. A continuous section of tubing 217 (comprising, e.g., extrudedinner layer 24 and outer layer 26 with an embedded braided mesh 25, asdescribed above) is placed over the beam, as illustrated in FIG. 11B.The tubing 217 has a sufficient length to cover the beam longitudinallyand a suitable diameter that is large enough to accommodate all widthsof the beam. Where the beam has a plurality N of cylindrical bodies 266,a plurality of at least (N+1) heat shrink tubings 270 are placed overthe tubing 217 with ends of adjacent tubes 270 abutting at or near amidpoint of each cylindrical body 266. The heat-shrink tubings 270 maybe fluorinated ethylene propylene (FEP) or polyethylene terephthalate(PET). Each heat shrink tube 270 may have a distinct diameter thatcorresponds with the width(s) of the section(s) 230 or 231 it covers. Inthe illustrated embodiment of FIG. 10, there are three heat shrinktubings 270D, 270M and 270P, with respective diameters DD, DM and DPwherein DD<DM<DP.

The heat shrink tubings 270 are recovered by application of heat (e.g.,by a heat gun) and then placed in a two-piece heat fusing die head (notshown) for heating to reflow the tubing 217 of the deflectable section14, which conforms the tubing 217 to the cylindrical brackets 266A and266B and fuses the inner layer 24 to the brackets by means of meltedmaterial flowing into perforations 268 to form nodes interlocking thetubing 217 and the brackets 266A and 266B. Textured side edges E1 and E2of the beam 230 also help minimize slippage between the beam 230 and thetubing 217. Thereafter, the heat shrink tubings 270 can be removed fromthe tubing 217.

Alternatively, the tubular structure 17 of the deflectable section 14may be constructed by injection molding, instead of extrusion andreflow.

In the illustrated embodiment of FIG. 1, the distal assembly 15comprises a generally straight proximal region and a generally circularmain region having at least one loop circling about 360 degrees, if nottwo loops circling about 720 degrees. The proximal region is mounted onthe deflectable section 14 and the main region carries a plurality ofelectrodes (ring and/or tip) for mapping and/or ablation. With referenceto FIG. 5, the distal assembly 15 includes the shape memory supportmember 72, lead wires 140 for the electrodes carried on the distalassembly 15, and a cover 120 extending the length of the distalassembly. The lead wires 140 attached to the electrodes on the distalassembly 15 extend through a nonconductive sheath 141 which extends fromthe distal assembly through the lumen half 19B of the deflectablesection 14, through the cavity half 67B of the transition section 65,through the lumen 18 of the catheter shaft 12, and into the controlhandle 16. Ring electrodes may also be carried on the deflectablesection 14, as shown in FIG. 3.

An electromagnetic position sensor 134 (FIG. 5) is mounted in or nearthe distal end of the deflectable section 14 or the proximal end of thedistal assembly 15. A sensor cable 136 extends from the sensor 134 intothe half lumen 19A of the deflectable section 14, the cavity half 67B ofthe transition section 65, the central lumen 18 of the catheter body 12and into the control handle 16 where it terminates in a suitableconnector (not shown).

The catheter 10 may also be adapted for irrigation at the distalassembly 15, for example, to supply fluid at or near the electrodes ofthe distal assembly. To that end, an irrigation tubing 150 may beprovided to pass fluid to the distal assembly 15 from the control handle16. In the illustrated embodiment of FIG. 2, the tubing 150 passesthrough the central lumen 18 of the catheter body 12, the lumen 19 b ofthe deflectable section 14, and into the distal assembly 15.

In use, a suitable guiding sheath is inserted into the patient with itsdistal end positioned at a desired location. An example of a suitableguiding sheath for use in connection with the present invention is thePreface™ Braiding Guiding Sheath, commercially available from BiosenseWebster, Inc. (Diamond Bar, Calif.). The distal end of the sheath isguided into one of the chamber, for example, the atria. A catheter inaccordance with an embodiment of the present invention is fed throughthe guiding sheath until its distal end extends out of the distal end ofthe guiding sheath. As the catheter is fed through the guiding sheath,the distal assembly 15 is straightened to fit through the sheath. Oncethe distal end of the catheter is positioned at the desired location,the guiding sheath is pulled proximally, allowing the deflectablesection 14 and distal assembly 15 to extend outside the sheath, and thedistal assembly 17 returns to its original shape due to itsshape-memory.

The user manipulating the actuator 13 on the control handle 16 actuatesdeflection mechanism inside the control handle 16 to draw puller wireproximal portion 28A or 28B to deflect the distal section 14 on-plane toone or the other side of the beam 30. The user may then rotate thedistal assembly 15 by rotating the control handle 16 which transferstorque to the catheter body 12 and the deflectable section 14 throughthe transition section(s) 65. The brackets 66A and 66B to which thetubular structures 11 and 17 of the catheter body 12 and the deflectablesection 14 are bonded by means of interlocking nodes formed in theperforations 68 of the brackets 66A and 66B under heat fusion.

Suitable materials for construction of the beam, the beam stiffenersand/or the half-cylindrical brackets include 50/50NiTi, titanium(Ti-6AI-4V), phosphor bronze 510, beryllium copper, monel alloy K-500 orMP35N (a non-magnetic nickel-cobalt-chromium-molybdenum alloy). Suitablematerials for the puller wire include preformed, heat treated and TEFLONcoated NiTi wire, monel alloy K-500 or dual VECTRAN fibers.

Suitable materials for imbedded braided mesh for the tubular structuresof the catheter body and/or the deflectable section include stainlesssteel (304V or 316), phosphor bronze, monel K-500, PEN or othersynthetic fibers that can readily bond with PEBAX or PELLETHANE extrudedthermoplastics during the secondary/outer extrusion coat or layer.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. As understood by one of ordinary skill in the art, thedrawings are not necessarily to scale. Accordingly, the foregoingdescription should not be read as pertaining only to the precisestructures described and illustrated in the accompanying drawings, butrather should be read consistent with and as support to the followingclaims which are to have their fullest and fair scope.

What is claimed is:
 1. A catheter, comprising: an elongated catheterbody comprising a first tubular structure having a first central lumen,a distal end and a proximal end; a deflectable section having a secondtubular structure having a second central lumen, a distal end, and aproximal end that is distal of the proximal end of the catheter body; aflat beam having first and second opposing surfaces, a distal end and aproximal end; the flat beam extending through at least the secondcentral lumen of the deflectable section, the flat beam defining a firstsub-lumen and a second sub-lumen; a puller wire configured with firstand second puller wire segments and a U-bend puller wire segmenttherebetween, the U-bend puller wire segment being anchored to thedistal end of the flat beam, the first puller wire segment extendingthrough the first sub-lumen and through the first central lumen of thecatheter body, the second puller wire segment extending through thesecond sub-lumen and through the first central lumen of the catheterbody; a first compression coil surrounding a portion of the first pullerwire segment extending through the catheter body, a second compressioncoil surrounding a portion of the second puller wire segment extendingthrough the catheter body; a pair of first and second half-cylindricalbrackets, the first half-cylindrical bracket comprising a firstinwardly-extending flange mounted on the first opposing surface of thebeam, the second half-cylindrical bracket comprising a secondinwardly-extending flange mounted on the second opposing surface of thebeam, the first and second half-cylindrical brackets forming a hollowbody generally surrounding the beam at or near a junction between thecatheter body and the deflectable section, wherein the distal end of thefirst tubular structure covers a proximal portion of the hollow body andthe proximal end of the second tubular structure covers a distal portionof the hollow body, and wherein the first and second inwardly-extendingflanges extend into a lumen generally defined by the pair of first andsecond half-cylindrical brackets.
 2. The catheter of claim 1, whereineach of the first and second half-cylindrical brackets has a G crosssection.
 3. The catheter of claim 1, wherein each of the first andsecond half-cylindrical brackets has two longitudinal edges extendingalong a length of a respective one of the half-cylindrical brackets, onelongitudinal edge is unattached and the second longitudinal edge isadjoined to a respective one of the first and second inwardly-extendingflanges, and wherein the first and second inwardly-extending flanges areeach affixed to a respective opposing surface of the beam.
 4. Thecatheter of claim 1, wherein each of the first and secondhalf-cylindrical brackets has at least two holes, and each of the firstand second tubular structures has an inner layer with at least oneinterlocking node extending into a respective hole in each of the firstand second half-cylindrical brackets.
 5. The catheter of claim 1,further comprising a first spacer extending along the first opposingsurface of the beam, the first spacer surrounding a portion of the firstpuller wire segment extending along the first opposing surface of thebeam generally between the proximal end of the beam and the distal endof the beam, and a second spacer extending along the second opposingsurface of the beam, the second spacer surrounding a portion of thesecond puller wire segment extending along the second opposing surfaceof the beam generally between the proximal end of the beam and thedistal end of the beam.
 6. The catheter of claim 1, wherein the beamgenerally bisects the second central lumen such that the first sub-lumenis a first lumen half and the second sub-lumen is a second lumen half,the flat beam having a neutral bending axis and being adapted to deflectin two opposing directions from the neutral bending axis, the distal endof the flat beam being at or near the distal end of the second tubularstructure of the deflectable section, and the proximal end of the flatbeam extending into the distal end of the first tubular structure of thecatheter body.
 7. The catheter of claim 1, wherein the beam haslongitudinal side edges with friction-inducing surfaces.
 8. The catheterof claim 1, wherein the distal end of the beam has a slit receiving theU-bend puller wire segment.
 9. The catheter of claim 1, wherein thedistal end of the beam has a through-hole receiving the U-bend pullerwire segment.
 10. The catheter of claim 1, wherein the puller wire has agenerally round cross-section.
 11. The catheter of claim 5, wherein atleast one of the first and second spacers includes an extruded tube. 12.The catheter of claim 5, wherein each of the first and second spacersmaintains a predetermined separation distance between the respective oneof the first and second puller wire segments and the beam.
 13. Thecatheter of claim 1, wherein the first tubular structure has a layer ofthermoplastic material, and the second tubular structure has a layer ofthermoplastic material.